Transmission regulation



C. W. GREEN TRANSMISSION REGULATION Dec. 15, 1925. 1,565,925

Filed Jan. s1 1925 /6 y 7 ANIM-W- l M AVA AVA' E Patented Dec. 15, 1925.

i 1,565,925 UNITED STATES `PATENT OFFICE.

CHARLES W. GREEN, F MILLBURN, NEW JERSEY, ASSIGNOR, BY MESNE ASSIGN- MENTS, TO WESTERN ELECTRIC `COMPANY, INCORPORATED, A CORPORATION 0F NEW YORK. TRANSMISSION REGULATION.

i Application led January 31, 1925. Serial No. 5,969.

To all 'whomz't may concern." n

Be it known that 1,/ CHARLES W. GREEN,

a citizen of the United States of America,

residing at Millburn, in the county of Essex and State of New Jersey, have invented certain new and useful Improvements in Transmission Regulations, of which the following is a full, clear, concise, and exact description. y

.10' This invention relates to transmission regulation and is particularly adapted foruse in carrier current signaling systems.

An ob]ect of the invention is to maintain the transmission efficiency of a carrier signal- '16 ing system constant.- under varying conditions.

Another object of the invention is to increase the sensitivity of transmission regulating systems.

The invention is particularly applicable to signaling systems employing fairly high frequencies in which, as is well known, the

transmission characteristics of the transmis-- sion medium `are subject to variations which render it difficult to maintain uniform signaling conditions.

Changes in the attenuation of the transmission inedium ofa systemv of this type'p-ro.

duce corresponding variations in the overall transmission equivalent of the system, and result in large fluctuations in the volume of a telephone orv other message being transmitted.v

In order to overcome the effects of transi mission variations in such systems, it is common practice to subject a pilotfrequency to the same conditions as those affecting theV i rvention a pilot frequency is transmitted between theterminals of a multiplex si aling system, and the second harmonic of t is frequen'cy is utilized to operate an automatic ,compensator inthe transmission line at a repeater or other oint inthe system.

In the preferre embodiment of the invention the second harmonic of the pilot frequency is picked up in the common output lead of a push-pull repeater amplifier and utilized to control a potentiometer in the repeater input ircuit.

Increased sensitivity is obtained by using the second harmonic of the pilot frequency in accordance with the invention, as the a-mplitude of the second harmonic will vary as the square of the amplitude of the pilot frequency.

The invention will be described as applied to a repeater for use in multiplex carrier current telephone or telegraph systems, but it isto be understood that it-may also be applied to other places in the system than at repeater points, and to various types of systems other than multiplex carrier signaling systems. f

`The various features and advantages of the invention will appear from the following description taken in connection with the accompanying drawing, which shows a circuit diagram illustrating the invention.

VThe drawing shows a one-way repeater adapted to couple two transmission line sections W and E. The signaling waves incoming at the repeater from line section W are amplified in the repeater and the amplified waves are delivered to line section E.

`The repeater may be. of any well known l type such as the balanced amplifier described in connection with Fig. 21 ofan article entitled Carrier current telephony and telegraphy by Messrs. Colpitts and Blackwell,

published in the Transact-ions of the American Institute of Electrical Engineers, volume 4o, 192i. n As illustrated, the balanced amplifier comprises a pair of three-element electron discharge tubes l and 2. Parallel input circuits having a common path 3 and individual pat-hs 4 and 5 are connected between the filaments and grids of the two tubes. The line section W is coupled to the input 'circuits through a transformer 6. Parallel output circuits comprising a common path 7 and individual paths 8 and 9 are connected be" tween the filaments and plates of the tubes, the output circuits being coupled to line section E through a` transformer 10.

In addition tothe signaling frequencies which are adapted to be amplified in the repeater, ^a pilot current is also impressed upon the line section W in the usual manner at the distant terminal, not shown. The second harmonic of the pilot frequency is picked up across a resistance 11 in the comj mon output path 7 where the level of second selected harmonic of the pilot frequency is then amplified in an amplifier 13 and rectified by means of a rectifier lt'of any well known type. A. voltmeter relay 15 in the output of the rectifier'lt is controlled by the rectifier currents. A

The voltmeter relay 15 may be arranged with its armature so biased that the direct current flowing in the output circuit of the rectifier 14. when the 'transmission efficiency of linesection W is normal` will be just sulhcient to hold the armature at a neutral point against the tension of the biasingv means. An increase or decrease in the direct current in' response to an increase or decrease in the eciency of line section W will, therefore, result in shifting the armature to one `yor the other of its contacts.

1n order to adjust the transmission efficiency of the repeater, a potentiometer 16 is' included in the line section W on the in, put si'de of the repeater. This potentiometenmay be adjusted by means of an arm 17 which may be rotated by a motor 18. The motor 18 maybe energized from th-e power mains 19 and its circuits are controlled by means `of relays 20 and 21, so that when either of tlese relays is operated theKL armature circuit is closed, and when one of the relays is operated the field circuit is completed in one direction while when -the other relay is operated the field circuit is completed in the opposite direction.

Relays 20 and 21 are controlled by the contacts of the voltmeter relay 15 so that ifthe armature of the relayg15 is shifted to one contact, the motor 18 will rotate in one direction and adjust the potentiometer to increase the transmission, while if the arma- 'ture is shifted to the other contact of redecrease the transmission.

In describing the operation of the transmission regulating system, let it be assumed that the line section W increases in attenu`` ation so that the outputv level' of the repeater amplifier is correspondingly ,decreased. Under such conditions the pilot current incoming from line section QW is attenuated more than thernormal amount,

and the level of the second harmonic of the pilot frequency in the common path 'Y of the repeater amplifier is correspondingly decreased. Current in the output of rectifier le is therefore decreased and the voltmeter relay ,i5 be toclose one of its contacts, say the left hand contact, thereby energizing the relay 21. The operation of' relay 21 completes the field and armature circuits of the motor 18 to vcause the motor to rotate in one direction and ad' just the potentiometer 16 to gradually increase the gain of the amplifier until a condition isreached such that the amplitude of the second harmonic of the pilot frequency will be sufficient to produce `a rectified current in the rectifier 14 of'such value as to again shift the armature of the volt-A meter relay 15 tc a neutral position. j When such a'condition has beenreached the operation of the motor 18 will cease, the change in the transmission of the line section Wy having been compensated for by the increased gain of *the amplifier.

If the transmission ehiciency of the line section W isv increased, the pilot current incoming at the repeater is increased in amplitude, and the level ofthe second har lmonic of the pilot frequency inthe common path 7 is correspondingly increased. This causes a greater direct current to How through the voltmeter relay 15, shifting the armature to the right hand contact to energize the` relay 20. The operation of the relay 20 causes the motor 18 to rotate in the opposite direction and adjust the potentiometer 16 so that the gain of the repeater amplifier is gradually decreased. This results in a gradual decrease in the amplitude of the pilot frequency, and hence 0f the level of the second harmonic of the pilotfrequency, until a point is reached where the direct current flowing through the voltmeter relay 15 will be reduced to its 15 is shifted to neutral and the motor 18 stops' rotating.

It will be seen from the above that increased sensitivity is obtained by using the second harmonic of the pilot frequency to control the gain and level of the repeater amplifier', as the amplitude of the second harmonic lwill vary as the square of the amplitude of the pilot frequency. Hence, this regulatin system seryes to compensate for very'smal changes' in the transmission of the system, and the system is automatically adjusted to operate at its maximum efficiency at all. times. l v

The invention set forth herein is, of course,'susceptible of various other modi .fications and adaptations not specifically referred to', but included within the scope of'- the appended claims.

What is claimed is:

'1. rlhe method of transmission regulation i which comprises transmitting` a wave over a variable transmission medium, producinga harmonic of said wave, and utilizing said harmonicto control the transmission efhciency of said medium.

2. The method of regulating the transmission of a variable transmission medium over which carrier Waves are transmitted, which comprises selecting the second"harmonic of one of said waves, and controlling an element in said transmission medium in accordance with the amplitude of said harmonic.

3. The method of regulating the transmissionrof a variable transmission medium over which carrier waves are transmitted which comprises selecting the second harmonic of one of said waves, rectifying the selected harmonic, and controlling an elementin said transmission medium in accordance with the rectified current.

4. In a signaling system in which a plurality of signaling waves are simultaneously transmitted over a variable conducting path, the method of maintaining a constant transmission equivalent which consists in subjecting a pilot Wave to substantially the same conditions causing attenuation as those affecting the signaling waves, deriving a harmonic of said pilot Wave, and controlling an element in said conducting path in accordance with the amplitude ofsaid harmonic.

5. In a signaling system in which a plurality of signaling waves are simultaneously transmitted over a variable conducting path, the method of maintaining a constant transmission equivalent which consists in subjecting a pilot Wave to substantially the same conditions causing attenuation as those affecting the signaling Waves, deriving the second harmonic of said pilot Wave, rectifying said harmonic, and controlling an element in said conducting path in accordance with the rectified current.

6. In a system of transmission regulation, a variable transmission medium over which carrier Waves are transmitted, means to derive a harmonic of one of'said Waves, and means controlled by said harmonic to regulate the transmission of said medium.

7. In a system of transmission regulation, a variable transmission medium over which a pilot Wave is transmitted, means to derive thesecond harmonic frequency of said pilot Wave, and means controlled by said harmonic frequency to regulate the transmission of said medium.

8. In a system of transmission regulation, a variable transmission line over which a pilot wave and signaling Waves are transmitted, a potentiometer in said transmission line, means to derive a harmonic frequency of said pilot wave, and means controlled by said harmonic frequency to adjust saidpotentiometer lwhen the transmission of said line departs from normal.

9. In a system of transmission regulation, a variable transmission line over which a pilot Wave and signaling Waves may be simultaneously transmitted, an amplifier associated with said line, means to derive a harmonic frequency of said pilot wave, and means controlled by said harmonic frequency to adjust the gain of said amplifier.

10. In a system of transmission regulation, a variable transmission line over which a pilot Wave and signaling waves may be simultaneously transmitted, a repeater associated with said line, a potentiometer in the input circuit of said repeater, means to derive a harmonic frequency of said pilot wave, and means controlled by said harmonic frequency to adjust said potentiometer when the transmission of said line departs from normal.

11. In a system of transmission regulation, a variable transmission line over which a pilot Wave and signaling Waves may be simultaneously transmitted, a repeater comprising a balanced amplifier associated with said line, a potentiometer in the input circuit of said amplifier, means in the output circuit of said amplifier to select a harmonic frequency of said pilot wave produced by modulation in said amplifier, and means controlled by the selected harmonic frequency to adjust said potentiometer when the transmission of said line departs from normal.

12. In a system of transmission regula- .tion, a variable transmission line over which a pilot Wave and signaling waves may be simultaneously transmitted, a repeater comprising a balanced amplifier associated with said line, a potentiometer in the input circuit of said repeater, a selective circuit for transmitting the second harmonic frequency of the pilot wave produced by modulation in the output of said balanced amplifier, means to produce from said selected harmonic frequency a direct current whose amplitude depends upon the transmission conditions to which the pilot Wave has been subjected, and means controlled by said direct current to adjust said potentiometer to compensate for the change in transmission eficiency of said transmission line.

In witness whereof I hereunto subscribe my name this 28th day of January A. D., 1925.

CHARLES W. GREEN. 

